November 15, 2005

Tamoxifen curbs breast cancer risk, study confirms

by ssavage

NEW YORK (Reuters Health) - Data from additional years of
follow-up of a large study of tamoxifen for the prevention of
breast cancer confirm that the drug reduces the risk of the
disease in high-risk women.

Tamoxifen "remains the only proven chemopreventive
treatment for breast cancer risk reduction," Dr. Bernard
Fisher, from the University of Pittsburgh, and colleagues note
in their report in the Journal of the National Cancer Institute
this week.

In the study, which began in 1992, a total of 13,388 women
aged 35 years or older who were at high risk for breast cancer
due to family history and other factors were randomly assigned
in a blinded fashion to receive either a placebo or tamoxifen
for 5 years.

In 1998, when the study was "unblinded," researchers
observed that women taking tamoxifen had a 49 percent lower
risk of developing breast cancer.

Tamoxifen was also found to reduce the risk of osteoporotic
fractures but to increase the risks of endometrial cancer and
thromboembolism (blood clots).

At the time the study was unblinded, the women who were
taking placebo were given the option of starting tamoxifen.

The latest data from the trial reported this week shows
that the benefits and most undesirable effects of tamoxifen
remain. That is, after 7 years of follow-up, using tamoxifen
rather than placebo reduced the cumulative rate of invasive
cancer by 43 percent, from 42.5 cases per 1,000 women in the
placebo group to 24.8 cases per 1,000 women in the tamoxifen
group.

The rate of noninvasive breast cancer was reduced by 37
percent, from 15.8 cases per 1,000 women in the placebo group
to 10.2 cases per 1,000 women in the tamoxifen group. These
changes were similar in magnitude to that seen in the initial
report.

Tamoxifen use was also associated with a 32 percent
reduction in the risk of fractures, the findings indicate.

In general, tamoxifen raised the risk of adverse events,
such as blood clots and cataracts, to a similar extent as in
the initial report. The exceptions were a lower risk of
developing blood clots in the lungs and a higher risk of
endometrial cancer, but the differences fell short of
statistical significance. The risk of lung blood clots was
about 11 percent lower and the risk of endometrial cancer was
about 29 percent higher than first reported, but, again, these
differences were not significant.

According to Fisher and colleagues, a series of breast
cancer prevention trials now in progress are evaluating other
agents that "could be more effective than tamoxifen in curbing
the risk of breast cancer and reducing the frequency of
undesirable side effects noted with the drug."

However, "until one of these trials demonstrates a greater
net benefit from an alternative therapy, tamoxifen remains the
only proven chemopreventive treatment for breast cancer risk
reduction."